CA2472256C

CA2472256C - Femoral head assembly with variable offset

Info

Publication number: CA2472256C
Application number: CA2472256A
Authority: CA
Inventors: Joseph Saladino; Mark E. Nadzadi; Brian Burkinshaw
Original assignee: Zimmer Inc
Current assignee: Zimmer Inc
Priority date: 2003-07-03
Filing date: 2004-06-25
Publication date: 2010-05-11
Anticipated expiration: 2024-06-25
Also published as: AU2004202928A1; EP1506751A2; JP2005028129A; EP1506751B1; US20050004680A1; AU2004202928B2; ATE427721T1; US7833277B2; US7306629B2; CA2472256A1; EP1506751A3; US20080058951A1; DE602004020431D1

Abstract

A proximal femoral head assembly having a variable offset that is selectively adjustable to conform to various anatomical conditions encountered during a femoral surgical procedure. The assembly includes a femoral head, a neck removeably connectable to the femoral head, and an adjustment mechanism. The adjustment mechanism provides the neck with a plurality of different femoral offsets with respect to a femoral hip stem.

Description

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Meld of the Invention 'The disclosure generally relates to implantabie orthopaclic prostheses for total hip arthroptasty and, n~or~ particularly, to a proximal femoral head assembly having a variable offset that is setectlvety adjustable to conform to various anatomical condifiions encountered during a femoral surgical procedure.
14 Icground of ~e Invention t3uring a total hip arthroptastyr, a femoral stem is implanted into the intramedullary canal of a femur. After the stem is inserted to the proper depth and orientation, a femoral head or bait is attached to the proximal end of the stem. 1'his head fps into the socket of an acetabutar component and provides a joint motion surface for articuta#ion between the femoral prosthesis and aoetabuium. A neck or trunian extends between the femoral bats and stem. in many embodiments, this neck generally has a cylindrical configuration with one end connected to the belt and one end connected to i~he stem.
Several c~Caf features are important to ensure that the femoral hip prosthesis property functions once implanted ire the femur. Une of these features is the femoral head offset." Femoral offset is horizontal distance from the center of rotation of the femoral head do a line bisecting the long axis of the femur from a standing A P x-ray. Similarly, the ott of the proximal femoral cx~mponent of a hip prosthesis is the horizontal distance from the enter of rotation of the femoral head to the long axis of the stem.
t7ne important decision that must be made during hip surgery is how much offset should occur between the teimoral ball and stem, If the ofl'set does not match the natural anatomi~cat needs of the patient, n the prosthesis ran be r~t~OrnE3yl ~,: I~t-4~J:~
pa~itior~ toQ far laterally or mad~tly» An unnecessary decrease in alt'set greatly ~ the sucxess and proper function of the hip implant after surc,~ry.
A decrease in femoral offset medially shifts or moves the femur closer to the pelvis. This decrease can result in impingement of the prosthesis far some S patients after surgery. A medial ship can also cause soft tissue surrounding the irr~plant to become loose or tax. Impingement and soft tissue Laxity can further lead to instability of the implant, subiuxation, and even dislocation. As a further disadvantage, when the offset d~reases, the abductor muscles utlize a greater force to balance the pelvis. This tncreassr in force rxeates a discrepancy that lU may result in a Limp for the patent. As another eonsequenre, the resultant faros across the hip ioint else increases, and this increase can t~tad to greater polyethylene wear between the femoral bait and prosthetic acetabuiar In contrast to a decreased offiset, an in~ease in fiemorat offset laterally 15 shills or moves the femur farther from ~e pelvis. In soma instance, an increase in oft is desirable. ''his intxease can reduce the risk of impingement and improve soft tissue tension, resulting in a more stable implant. iFurther, the addui~tor muscles can be more property batanc~d and improve the gait of the patient. Further, proper balance and alignment can teed to less wear and 20 loosening over tme.
Manufacturers and designers of femoral hip prosthesis recognize the shortcomings associated with decreased offset and endeavor to match the offset with the anatomical needs of the patent. tn order to remedy thesE:
shortcxamings, femora! hip prostheses are sold with different offsets. °fihe number .and d~ree of 25 difl'ercnt offsets vary between the manufacturers. A typical prosthetic system can include three to frve different offsets for each femoral haft size. For example, a manufacturer may provide femoral butts with offsets.of -~ mm, d mm, *4 mnr~, +8 mm, and +i2 mm. These offsets would be available far five or six different ball sizes. tn short, the manufacturer is required to have an inventory of 18 to 3~
30 different femoral heads.

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An inventory of femoral heads of this magnitude is enormous. t=urther, the tx~sts associated with maintaining and distributing this inventory are very great fior a company. This large inventory, then, is a r disadvantage.
As another important disadvantage, rnanufat~urers offer the femoral head offsets in fixed, discrete, large increments. As noted, the offsets', for example, may be offerted in incremertts of 4 mm, such as offsets ofi -~4 mm, 0 mm, +4 mm, +S mm, and *12 mm. These faced increments though may not exactly match the anatomical offset that the patient needs. for example, if the patient requires an offset ofi +8 mm, then the surgeon must choose between an offset of either +4 mm or +g mm.
tt therefore would be advantageous to provide a proximal femoral head having a variabhe offset that is selectively adjustable to conform to various anatomical conditions encountet9ed during a femoral surgical procedure.
I~
Sul~t~lary c~~ the Ihventic~rr The present invention is directed to impiantabte orthopedic prostheses fior iotat hip arthroptasty and, more particcirarly, to a proximal femora' ball assembly having a variable offset that is se~ly adjustable to conior~m to various anatomical conditions encountered during a fiemora! surgical procedure.
1"he femoral ball assembly generariy comprises a head, a neck, and an adjustment mechanism. The head has a smooth spherical outer surface that is adapted to engage an ac~tabular cxamponent or native acetabulum. The neck extends outward from the head and removeabty connects to t#te head using a threaded attachment.
The adjustment mechanism provides a variable offs~t for the femoral tai!
assembly. More spea'~'rcatty, the adjustment mechanism varies the Length that the neck protrudes from the head. As this Length increases, the femoral offset correspondingly increases, As this length decreases, the femoral offset 3U correspondingly decreases. One important advantage then is that the surgeon can intro-operatively select from a wide array of femoral of~ets. 't'hese offsets ,t:
_'~ttoimey ~oc.:1~1-453 can be provided with a small number of components. As such, a large, expensive inventory of differently sued femoral bails with diffa~nt offsets is not necessary.
Another advantage of the present invention is that a plurality of femoral S offsets can be offer~d in smelt increments. The offsets, for example, can be offered in 1 mm increments. These small incr~aments can be used to more closely match the natural anatomical needs of the patient. further, these offsets can be offered in a range from about -10 mm to about +10 mm, but a range of up to about +34 mm is within the scope of the invention.
In another exrrbodiment, a fen~~orat halt system is provided. The system has a pluralitjr of differently sued femoral heads and spacers. These heads and spacers can be utilized with a single neck to provide a multitude of femoral offsets with a plurality of differently sized spherical heads or bails.
In yet another embodiment, two separate axes extend through the femoral ball assembly. A first axis ar central axle is concentric with the body of the spherical head, and a second axis or eceer~tric axis is conc~en~rie with the threaded bore of the head. This second axis rs also concentric with the adjustment mechanism and neck of the femora! ball assembly. These two axes are parallel to each other and form an acute angle with the Longitudinal axis of 2~ the stem.
Brief' Descriptren of the Drawings FIG. '9 is an exploded view of a femoral hip stem, an assembled fiemoral ball assembly according to the invention, and an acetabuiar component.
~'tG. 2 is an exploded view of the femoral ball assembly according to the invention.
piG. 3 is an exploded view of an alternate embodiment of the femoral ball assembly.
~tG. 4 is an exploded view of an aN~emate embt~diment of the femoral ball 3o assembly.

it _~tomey Dac.: iOt-453 FtG. 5 is a~ exploded view of a femoral ball system according to the invention.
FIG. 6 is an exploded view of an alternate embodiment of the femoral bait assembly.
FtG. 7 is an exploded view of another embodiment of the femoral ball assembly.
FIG. 8 is an exploded view of yet another embodiment of the femoral ball asse~nbty.
FtG. 9 is an enlarged perspective view of the assembt~ femoral ball 1U assembly of FIG. 8, FIG. 90 is an exploded view of another embodiment of the femoral ball assembly.
is Detailed IDeacription L.oaking to FIG. 1, an imptantable orthopedic femoral hip stem or implant 10, a proximal femoral head or ba!! a$sembly 12 atxording to the invention, and an acetabuiar component 1~ are sho~m. These components are ~nnectabte together for uge in a totat hip arthroplasty.
20 Stem 10 includes a b~iy 20 that extends from a proximal region 22 to a distal n~gion 24. A iortgitudina! or tong axis 25 extends through the body.
'The body tapers downwardly and generally has a cylindrical or trapezoidal shape with the distal end being rounded to facilitate insertion into the intracx~lullary canal of a femuir. fibs proximal region '22 includes a proximal body portion or ttochanteral 25 portion 2~ having a cyttndcica! 'bore 28, a collar 30, and a top surface 32. A neck 34 extends outwardly from the top surface 32. 'f'he neck 34 has a tapered body that connects to the femoral ball ambly 12.
The acetabular componbnt 14 is configured to ft in the acetabulum of a patient and is formed from an outer shaft ~0 and an inner liner or bearing 3o component 42. The shelf is generally shaped as a hemispherical cup defined by an outer hemispherical surface or bone engaging surface and an inner - '~torney Doc.: it~l-453 hemispherical surface connected to the bearing component. The outer surface can be porous or textured white the inner surface is smooth and adapted to articulate with the femoral halt assembly 12.
One skilled in the art will appreciate that the femoral ball assembly of the present invention can be employed with various implants and implant designs without departing from the scope of the inven5on: The stem fit?, #or example, can be the Apolla~ Hip or Naturat~" Hip manufactured by Denterputse Carthopedics tnc. of Austin, Texas; and the acetabutar component 14 can be the AilofrtTM ar Canverge"~' ar~tabutar system manufactured by the same company.
Looking now to FI~;S.1 and 2, the fiernoral bait assrrmbly 1~ is adapted to connect at one end to the femoral hip stem 10 and at another send to the acetabular component 14. The femoral bail assembly 92 comprises a head 5~, a neck 5~, and an adjustment mechanism 54. A central axis 55 extends thr9augh the center of the head, the neck, and adjustment mechanism.
Head 50 has a body that is shaped as a partial sphere. This body has a smooth outer surtace 50 adapted to engage and siideably articulate with the bearing component 42 of the acetabutar component 14. A collar or tapered transition 62 circmmrferentiatly extends around a base fi4 of the spherical body. A
threaded and cylindrical bore 56 extends into the body.
2d Neck 52 has a generally straight cylindrically shaped body that extends from a first end ?0 to a second end ?2. The first end ?0 inatudes a bore ?4 adapted to receive and engage neck 34 of stems 10. ~pecificatly, bore ?4 has a tapered cylindrical shape with smooth inner wads. This. taper is adapted to fom~ a Morse taper connection with neck 34 when stem 10 and femoral ball assembly 1 ~ are connected together. Preferably, bore ?4 does not extend completely through neck 52 but stops at a generally planar end surFace ?G Shawn as dashed tines inside the body. The second end ?2 includes an ext~matly threaded se~ion ?8. This threaded s~:tion is adapted to threadably engage with threaded bore 65 of head 50.
3o Adjustment mechanism 54 is adapted to vary the effective length "L"
(shown in FIG. 1 ) of neck 52 extending outwar~cfly from head 50. Effective length ~ttomey t3oc.: I~I-453 "L° extends from fcrrst and 70 to base 64 of the body of the head 5~.
Adjustment mechanism 54 is further adapted to pa variable "offset" between the femoral head assembly 12 and femoral stem 1~. t=amoral offset is the horiaorrtat distance from the center of rotation of the femoral head to a line bisecting the S long axis 25 of the femur from a standing A-I~ x-.ray. Similarly, the offset of the proximal femora! component of a hip prosthesis is the horizontal distance from the center of rotation of the femoral head to the long axis of the stem.
As shown in EIG. 2, adjusbnent rr~echanism 5~. includes a spaa~r 80. This spacer has a short cylindrical shape and is preferably formed as a sorrd round or 1 U coinrshape. ~paoer 80 is adapted to b~ removeably positioned in bore 85 of h5f~.
An adjustment mechanism of the present invention may be used in various ways to provide a variable offset between the femoral head and femoral stem. IFtG. 2 shows one example. White spacer 80 is removed from the bore 86, 15 neck 52 can be threadabty connected to head 50. Once the neck is fully seated and dreaded into bore 88, the neck 52 wail have an effective length L1. This Length ~uaJs the distance from first end ?0 to base 64 of head 50. Neck 52 can be removed from head 50 and spacer 80 then placid inside of bore 88. Spar 8tt has a thickness equal to T. With the spacer 8tf pieced in bore 88, neck 52 20 can be threadably connected to head 50. dnce the neck is fully seated and threaded into bore 86, the neck 52 will have an efieGtive length L2, when:in L2 =
L1 + T. 1n other words, the spacer lengthens the distance from first end ?0 to base fi4 an amount equal to its thickness T.
The embodiment in SIG. 2 is able to provkle a femoral baH with two 2S differrent offsets between the femoral head and femoral stem. The length difference between these two offsets depends on the sickness of the spacer.
The spacer can be sized to have various thickness. As such, the offset can be varied lay varying the thickness of the spacer. Further, a piural~y of spacers with different thicknesses can be provided. !~or example, these spacers could have 30 thicknesses with one millimeter increments, such as 1 mm, 2 mm, 3 mm, 4 mm, .'~torney Doc.: It71..453 nun, 5 mm, etc. Other incrnts, of course, are within the soaps of ire irnrentnan.
J~tGS.1 end 2 show a I~torse taper connection between t!~ neck 34 of stem 10 and neck 52 of femoral bait 12. In this connection, neck 52 functions as S the female component and neck 34 functions as the male component. One skilled in the art watt appreciate that this connection can be altered and stilt within the scope of the invention. for exempts, neck 34 can be formed with a bare to function as the female component, and neck 52 can be formed as a solid tapered cylinder to function as the mate component. Various types of other connections 1 o could also be emptoyecl to connect the item to femora! ball assembly and stilt remain within the scope of the invention, These cdnnectivns include, but are not limited to, press~ftt connections, locking rings, radial or expandable devices (such as sleeves car ootlars), nitinot or other super~ela~stic materials, taper connections, locking connections, various polygonal connections (suds as. triangular, square, hexagonal, or trapezoidal), and the like. trt short, various ways can be used to connect the femoral bait 12 to the stem 10.
Looking now to tw'l0. 3, an alternate femoral bail assembly 100 is shown and includes a head 102, a neck 104, and an adjustment mechanism 1Q6. Head 102 and neck 10.4 are identic,~t to head 5a and neck 52 described in connection with ptGS. 1 and 2. tn FtG. ~, adjustment mechanism 105 includes two spacers 110 and 112. Preferably, these spacers have different thicknesses. These thicknesses, for example, can be seteoted from a group with one or iwo millimeter increments, such as 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 5 mm, etc.
Looking now tv t=tt~. 4, an alternate femoral ball assernbty 120 is shown and includes a head 122, a neck 124, and an adjustment medianism 12C. Head 122 and neck 124 are identical to head 50 and neck 52 described in connection with DIGS. 1 and 2. in t=tG. 3, adjusinnent rrrechanism 125 includes three spacers 130,132, and 134. Preferably, these spacers have d'rffer~:nt thicknesses. These thicknesses, for example, can be selected from a group with one or two miliimefier increments, such as 1 mm, 2 mm, 3 mm, 4 cram, 5 t~rrm, mm, etc.

-' .',~ C~oc.:1f,~1.~53 FIGS. 3 and 4 off~r a multitude of different offsets between the femoral head aril femorat stem. The affsets depend on the number and thickness of spacers used. Further, these spacers can be used alone (i.e., one spacer placed inside #~e bore of the femoral head) or used in conjunction with other spacers. tn the utter scenario, two, three, four, or more spacers can be stacked on top of each other' and then placed in the bore of the femoral head. This stacking arrangement can provide a wide range of k~ft'sets in smelt increments. Looking to FtG. 4 to illustrate an exempts, spacer 930 can haws a thickness of 1 mm;
spacer 132 can have a thickness of 2 mm; and spacer 134 can have a thickness of 4 mm. These spacers could be used, alone or in stacked combinations with each other, to have ~ticknesses of t7 mm, 1 mm, 2 mm, 3 mm, ~ mm, 5 mm, 6 mm, or ? mm. Thus, these thn3e spacers can provide a femoral bail with 8 different offsets, assuming one offset (~ mm) uses no spacer at alt.
Cane advantage of the present invention i$ that the number and thickness of spacers can vary to provide a multitude of offsets between the femoral head and femoral stem. As another example, four spacers could be provided to have thic~cnesses of 9 mm, 1 mm, 3 mm, and 6 mm. l"hese four spacers would allow iwehre different offset op8ons (U mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 5 mm, ?
mm, 8 rnm, 9.mrr~, 94 mm, and 11 mm). This e~camp~ is illustrated in ~'lt~. b.
t=iG. 5 shows a femoral belt system 150. system 150 includes a single neck 152, a plurality of femoral heads 9 54A, 1545, and 1 a4G, and an adjustment mechanism 156 having a pluratit~r of spacers 1 SBA, 158, 1586, and 158th. The neck, heads, and spacers are generally identical to the nedk, head, and spacer discussed in connection with FtGS.1 and 2. As one difference, the heads and spacers are offered in different sizes. Rr~eferabty, each head is sued differently, such as smelt, medium, and Large. More specifically, a plurality of heads could be provided to have outer diameters of 22 mm, 26 mm, 28 mm, 32 mm, 38 mm, and 44 mm. Further, the spacers can be sized to maximize the number of different offsets white reducing the overall number of inventor components.
r'Jne such size combination is spacers having thicknesses of 1 mm,1 mm, 3 mm, and ,~tomey DOC.: i(~t.~453 8 mm, tine skilled in the art will appreciate that many variations in the number and sire of heads and spacers are within the scope of the invention.
~It~.1~ shows another embodiment of a femoral bail assembly 24tJ that includes a head 202, a neezk ~0~4, and an adjustment mechanism 206. Head 202 and neck 2U4 are generally sirttilar to head 50 and neck 52 dt~scribed in connection with FIG; . 1 and 2. In ~tG. 3, adjustment me~cchanism 20G includes a biasing member 210 that is adapted to be placed into the threaded bore 212 of head 202. Biasing member 21 A is shown as a coif spring, but one skilled in the art wilt a~rreciate that many types of biasing members are also available.
1:Q During use, the biasing member 214 ~ placed in boas 212, and then neck 204 is threadably engaged with head 202. As the neck screws into the bone, the biasing member provides a greater and greater ford against the neck. In turn, the torque required to screw the neck increases as it threads into the bore.
In one ~irr~nt, this torque can be calibrated to specific oft~t values. In other words, specific torque values ~.an correspond to speck offsets. In another embodiment, indicia or a plurality of calibration marks 22~ can be pieced on the surface of the neck. Preferably these marks correspond to distinct, finite offsets.
Markings cxfuld be given to illustrate five d'~ferent ~ in 4 mm ina~ments, such as -4 mm, D mm, +4 mm, +8 mm, and +12 mm. Cane skilled in the art will 2U appreciate that various indicia can ba~used to illustrate various offsets.
P1G. 7 shows another embodiment of a femoral ball assernbiy 300 that includes a toad 302, a neck 304, and an adjustment manism 306, Neck 304 and adjustment mechanism 306 are identical to the head and adjustment mechanism discussed in connection with FIGS. 1 ~- 4. Head 302 is similar to the head 5th discussed in canrn with DIGS. 1 and 2 with one important difference: Head 30;2 is eccentric. More speci~calty, the body of head 3a2 has a central axis 310 that passes through the center of the body. The body also has a second or ecx~ntric axis 312 that is parallel to thr~ central axis and passes through the center of threaded bore 3i4. The center of bore 314 is thus offset or ecx~ntr~ic with the central axis 310 of the body. As shown, the center of spacers 32~ and 322 and neck 304 are concentric with bore 314.
i.0 i .'~tomey Doc.: fC71-453 The embodiment in FiG. ? is advantageous because i~he neck 304 is eccentric or offset from the head 302. 'This eccentric neck provides an in~ease range of motion once connected to the femoral hip stem 10 (F1G. 1 ). This incxease in range of motion more fully emulates the anatomical movements of a s natural hip. Additionally, this increase in range of motion provides mare joint stability to the implanted prosthesis. Aa yet another advantage, the eccentric neck providers a femoral hip prosthesis that is less likely to experience impingement, subtuxation, or even dislocation.
!=tGS. 8 arxf 9 show art~ther ernbodimertt of a femoral ball assembly 400 1o that includes a head 402, a neck 404, and an adjustment mechanism 408. Head 402 is identical to the head 50 discussed in connection with FIGS. 1 and 2.
Neck 404 is similar to the neck 52 discusse~f in connection with FIGS. 1 acxi 2 with one important difference: Neck 404 includes a collar or shoulder 40? at Brat end 408.
This collar has a circular or ring-shape and extends outwardly frora~ an outer 15 surface 410 of neck 404.
The adjustment mechanism 4th accomplishes a similar funt~ion to the adjustment mechanism a4 discussed in connection with FIGS. 1 and 2, but the function is perf'orn~ed in a different way. More spea~cally, the adjustment mechanism 406 includes a plurality of spacers 412 and 414. These spacers 2fl have a ring-shape or C-clip shape. U~nlitce spacer 80 in FIGS. 1 and 2, spacers 412 and 414 ar~r not adapted to fit inside bore 420 of head 402. Instead, spoaoers 412 and 414 are adapted to fit around the second end 424 of neck 404. As best shown in FIG. 9, the spacers e~ctend through sec~and end un#1 they abut against collar 40?.
25 Adjustmeryt mechanism 406 is adapted to vary the effeck'Ne length of neck 404. As discussed in connection with FIGS. '1 and 2, the adjustment mechanism is further adapted to provide a variable offset between the femoral head and fiemorat stem. As shown in t=IG. 9, the effective length of the neck is increased by a distance "~" equal to the thickness of spacer 412 plus the thickness of 30 spacer 414. These spacers may have equal thicknesses or unequal thicknesses.
lI

:~tomey hoc. r 14r-453 FIGS. 8 and 9 show the spacers with a C«ctip shape. C?ne skilled in the art wilt appreciate that other conf~un~tions are within the sole of the invention.
Sy way of example, these confi~urations include a full ring-shape or retaining ring shape.
~'tG. 10 shows another embodiment of a femoral ball assembly 50n that includes a head 5Q2 and a neck 504. The head 5D2 and neck 5t?4 are similarly canf~ur~ed to the head 5D and neck v2 of FIGS. 't and 2 with several important differences. t=first, femoral bait assembly 5C1~ does not include a separate adjus~trnent mechanism. fore 50fi has an irrtematly threaded watt that extends l0 clang the entire depth of the bore. The neck can thread along the entire Length of the bore. Thus, the length oil' the neck can be varied a distance "t~~
approximately equal to the depth of the bore. Further, indicia or a plurality of calibration marks 510 can be ptac~ed an the outer surface of the neck.
t~refierably these marks correspond to distinct, finite offsets that the surgeon can view and read during a surgical procedure. tUlarktngs could be given to illustrate 5ve different offsets in ~4 mm increments, such as -9~ mm, Q mm, +4 mm, +8 mm, and +9~ mm. (?ne skilled in the art wilt appreciate that various indicia can be used to illustrate various offsets and increments.
!n arder to prevent, the neck from loosening once a desired offset is 2fl chosen, a locking mechan~rn can be used to prevent relative ratationat motion between the neck and head.
The femoral head assembly of the present invention may bc~ manufactured of a wade array of biocompatible matetiats that are known in the: art. These materials include ceramics, stainless sleet, titanium, and oob~tiE chrome alloys.
25 Further, the adjustment mechanism may be manutac~ur~ed from a broader range of materials, such as various e~tastomers known in the ark. Preferably, such an elastomer has a weft dellned, c~antrolted, and reprraduc~bie Poisson°s ratio that can be used to adjust and monitor the femoral offset by tightening or loosening the neck to a given toad or torque level.
3U iFIGS. 1-. 9 illustrate a fer'norat ball assembly wherein the head, neck, and adjustment mechanism are separate components that are rernoveabty ,..:J ', . '.~torney I.: lOt.~453 connectable to each rather. Other embodiments are within the arx~pe of the invention. For example, the adjustment mechanism could be permanently aonto the neck or head. Further, the components can be configured to not be removeable from each other once they are connected. Further yet, the invention can utilize various locking mechanisms to kip or maintain the neck within the head and prevent any unintentional loosening, Although illustrative embodiments have been shown and described, a wide range of modifu~tions, changes, and substitutions is contemplated in the foregoing disclosure; and same features oi; the embodiments may be employed I O wr~hout a conBSponding use of other features. Accordingly, it is appropriate that the appended claims be constnaed broadly and in a ra°tanner consistent with the scope of the embodiments disclosed herein.

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Claims

1. An assembly comprising a femoral head assembly connectable to a femoral hip stem, the assembly comprising:
a femoral head having a body with a spherical outer surface adapted to articulate within an acetabular component, said body of said femoral head having a threaded bore;
a plurality of spacers of varying thickness, at least one of said plurality of spacers adapted to be inserted into the threaded bore;
a first neck having an externally threaded portion and at least one of an external tapered portion and an internal bore defining a internal tapered portion, said externally threaded portion being adapted to be threadably engaged with said threaded bore of said body of said femoral head;
wherein said first neck is adapted to extend outwardly from said femoral head in various lengths, each length corresponding to the thickness of said at least one of said plurality of spacers inserted into the threaded bore; and a femoral hip stem, said femoral hip stem having a second neck including at least one of an external tapered surface and a tapered internal bore, said one of said external tapered surface and said tapered internal bore of said femoral hip stem sized to engage said one of said external tapered portion and said internal bore of said first neck to form a Morse taper connection between said femoral hip stem and said first neck.

2. The assembly of claim 1, wherein said thicknesses of said plurality of spacers are provided in increments of 1 mm.

3. The assembly of claim 1, wherein said plurality of spacers have at least three different thicknesses.

4. An assembly, comprising:
a femoral head having a body with an outer surface adapted to articulate with an acetabular component, said femoral head comprising an internally threaded bore;
a first neck having a first externally threaded end adapted to be threadingly connected to the internal threaded bore of said femoral head and a second end comprising at least one of an external tapered portion and an internal tapered bore;
a femoral hip stem, said femoral hip stem comprising a second neck having at least one of an external tapered surface and a tapered internal bore, said at least one of said external tapered surface and said tapered internal bore of said femoral hip stem sized to engage said at least one of said external tapered portion and said internal tapered bore of said first neck to form a Morse taper connection between said femoral hip stem and said first neck;
and at least one spacer adapted to be positioned within said internally threaded bore of said femoral head between said first end of said first neck and said femoral head, wherein said at least one spacer engages said first end of said first neck and a bottom surface of said internally threaded bore of said femoral head when said first neck is threadingly coupled and seated in said internally threaded bore of said femoral head, said first neck extending outwardly from said femoral head by a length that corresponds to a thickness of said at least one spacer positioned within said internally threaded bore.

5. The assembly of claim 4 wherein said at least one spacer has a thickness selected from 1 mm, 2 mm, 3 mm, and 4 mm.

6. The assembly of claim 4 wherein said at least one spacer comprises at least three spacers, each of said at least three spacers having different thicknesses.

7. The assembly of claim 1 further comprising a plurality of femoral heads, each of said plurality of femoral heads having a different outer diameter.

8. The assembly of claim 1 further comprising a plurality of femoral heads, each of said plurality of femoral heads defining a central axis extending through a center of said body, at least one of said plurality of femoral heads further comprising an eccentric axis extending through a center of said threaded bore, wherein said eccentric axis is parallel to and offset from said central axis.

9. The assembly of claim 1 wherein said threaded bore of said femoral head is sized to receive more than one of said plurality of spacers to vary an offset of said first neck from said femoral head.

10. The assembly of claim 4 wherein said at least one spacer comprises a plurality of spacers and wherein at least one of said plurality of spacers engages said first end of said first neck and another of said plurality of spacers engages said bottom surface of said internally threaded bore, and wherein said first neck extends outwardly from said femoral head by a length that corresponds to a combined thickness of said plurality of spacers positioned within said internally threaded bore.

11. The assembly of claim 4 further comprising a plurality of femoral heads, each of said plurality of femoral heads having a different outer diameter.

12. The assembly of claim 4 further comprising a plurality of femoral heads, each of said plurality of femoral heads defining a central axis extending through a center of said body, at least one of said plurality of femoral heads further comprising an eccentric axis extending through a center of said threaded bore, wherein said eccentric axis is parallel to and offset from said central axis.

13. The assembly of claim 4 wherein said at least one spacer adjusts a femoral offset of said femoral head with respect to said femoral hip stem.

14. An assembly comprising:
a femoral head having a body with a spherical outer surface adapted to articulate within an acetabular component;
a first neck adapted to engage said body of said femoral head to secure said first neck to said femoral head; and a plurality of spacers, each of said plurality of spacers having a thickness and an open center, wherein, with at least a portion of a component of the assembly positioned within said open center of said at least one of said plurality of spacers, said at least one of said plurality of spacers is captured between said femoral head and said first neck;
a femoral hip stem having a second neck configured to secure to said first neck, wherein, when said second neck is secured to said first neck, movement of said femoral hip stem relative to said first neck is prevented.

15. The assembly of claim 14, wherein said first neck further comprises at least one of an

16 external tapered portion and an internal bore defining an internal tapered portion, and said second neck of said femoral hip stem further comprises at least one of an external tapered surface and a tapered internal bore, said one of said external tapered surface and said tapered internal bore of said hip stem sized to engage said one of said external tapered portion and said internal bore of said first neck to form a Morse taper connection between said femoral hip stem and said first neck.

16. The assembly of claim 14, wherein said body of said femoral head further comprises an internal bore, wherein said first neck is sized for receipt at least partially within said internal bore, said first neck further comprising an annular collar extending outwardly therefrom, said first neck sized such that at least a portion of said first neck is positionable within said open center of at least one of said plurality of spacers, wherein, with at least a portion of said first neck positioned within said open center of said at least one of said plurality of spacers and said first neck at least partially received within said internal bore of said femoral head, said at least one of said plurality of spacers is captured between said femoral head and said annular collar.

17. The assembly of claim 16, wherein said internal bore of said femoral head further comprises a threaded bore and said first neck further comprises an external threaded portion configured to threadingly engage said threaded bore of said femoral head.

18. The assembly of claim 14, wherein said plurality of spacers comprise substantially ring-shaped bodies.

19. The assembly of claim 14, wherein said plurality of spacers comprise substantially C-shaped bodies.

20. The assembly of claim 14, further comprising a plurality of femoral heads, each of said plurality of femoral heads having a different outer diameter.

21. The assembly of claim 14, further comprising a plurality of femoral heads, each of said plurality of femoral heads defining a central axis extending through a center of said body, at least one of said plurality of femoral heads further comprising an eccentric axis extending through a center of said threaded bore, wherein said eccentric axis is parallel to and offset from said central axis.

22. The assembly of claim 14, wherein said first neck is sized to be positionable within said open center of more than said at least one of said plurality of spacers to vary an offset of said first neck from said femoral head.